1. Field of the Invention
The present invention relates to a bearing having a long working life in a corrosive aqueous acidic or alkaline solution or under the circumstance where mists or droplets of a corrosive aqueous solution are present.
2. Description of Related Art
Generally, a rolling bearing comprises an inner ring having an inner ring raceway on an outer circumferential surface, an outer ring having an outer ring raceway on an inner circumferential surface, a plurality of rolling elements disposed rotably between the raceways of the inner and the outer rings, and a cage for guiding and supporting the plurality of rolling elements between the raceways of the inner and outer rings. There is also a rolling bearing of a full type ball bearing structure not having any cage.
Such rolling bearing is usually lubricated by circularly supplying lubricant oil or grease to the bearing, or sealing the same to the inside of the bearing. In addition, it is necessary to prevent intrusion of mists and droplets of a corrosive aqueous acidic or alkaline solution to the inside of the bearing under the circumstance that such mists and droplets are present. For this purpose, Japanese Utility Model Unexamined Publication No. Sho 55-34002 and Japanese Utility Model Unexamined Publication No. Sho 57-56218 have disclosed techniques to fill lubricant or grease to a space of the bearing to conduct lubrication, as well as to dispose a contact type seal or a labyrinth seal to the bearing to prevent intrusion of water or the like to the inside of the bearing.
However, in the contact type seal, since the lip of the contact seal is worn along with the rotation of the bearing, a gap is sometimes caused between the lip and the seal surface, and intrusion of water from the gap can not be prevented completely. Also, the labyrinth seal can not prevent intrusion of water from the gap completely. Therefore, even if the contact type seal or the labyrinth seal is disposed, water intrudes into the bearing from the gap caused by the wear of the contact type seal and the gap of the labyrinth seal to soften the lubricant or grease, so that the lubricant or grease splashes during rotation to the outside of the bearing to possibly contaminate external circumstances of the bearing.
Accordingly, when clean circumstance is required such as in clean rooms, manufacturing apparatus for semiconductor devices, manufacturing apparatus for liquid crystal panels and manufacturing apparatus for hard disks, the lubricant and grease can not be used for the lubrication of the bearings.
Then, as a method of lubricating the rolling bearing, there has been proposed a method of not using an lubricant or grease. For example, Japanese Patent Examined Publication No. Hei 8-26894 and Japanese Patent No. 2709119 have disclosed a rolling bearing comprising inner and outer rings made of stainless steel, a cage made of fluoro-resin (consisting only of fluoro-resin or a tetrafluoroethylene-ethylene copolymer containing short fibers of potassium titanate whisker having a diameter of 2 .mu.m or less) and rolling elements made of hard carbon. In the bearing, the fluoro-resin constituting the cage transfers to the rolling element, the inner ring and the outer ring to form a thin lubrication film of the fluoro-resin by frictional contact between the cage and the rolling element.
However, the rolling bearing used in a corrosive aqueous solution or under the circumstance where mists and droplets of a corrosive solution are present can not be prevented completely from corrosion such as occurrence of rusts even if the inner ring and the outer ring are made of stainless steel. Since the corrosion accelerates the increase of wear and the surface roughness of the bearing constituent members, sufficiently long bearing life can not be obtained.
Namely, the rolling bearing comprising an inner ring and an outer ring made of stainless steel, a cage made of fluoro-resin and rolling elements made of hard carbon does not cause contamination of external circumstance by the lubricant, but it involves a drawback that it is difficult to maintain lubrication and obtain sufficiently long bearing life over a long period of time in a corrosive aqueous acidic or alkaline solution or under the circumstance where mists and droplets of an corrosive aqueous solution are present.